1. Field of the Invention
The present invention is directed to offshore structures which are fabricated at a point remote from the point where they are ultimately located. More particularly, the invention is concerned with a method and apparatus for unitizing an offshore jacket of extensive length for an offshore platform and locating same at a selected location. In its more specific aspects, the invention is directed to method and apparatus for use in extremely deep waters where an offshore platform is supported for various purposes such as, but not limited to, well drilling, production of oil and gas, storage of oil and the like, and supporting navigational aids and the like.
2. Description of the Prior Art
It has been known for many years that structures may be located in deep waters by making the structures buoyant and floating them to a selected location in a body of water either in an assembled or non-assembled condition. To accomplish this, however, where heavy seas may be encountered and long tows may be necessary, excess buoyancy, as much as 35 percent or more, must be built into the structure, which for a platform jacket or support in waters of 500, 750, 1000 feet or more may require flotation members each of which may be as large as a submarine.
It has also been known that flotation tanks may be added to sections of an offshore structure and the sections gradually added one on top of each other until the completed structure is above water level. Another possible method is to build an offshore structure close to land in shallow water or on land and add buoyant sections to it as the structure of increasing height is skidded or towed farther and farther to sea into deeper water until the desired location is reached.
It has been disclosed in the prior art that supporting members for offshore structures may be sealed by frangible or flexible (rupturable) diaphragms to maintain columns free of debris and to confer buoyancy thereto.
The art has also described the floating of an offshore structure to an offshore location on a barge and then launching it and sinking it at a selected point. This, too, is attendant with difficulties because the usual barge is only about 300 to 400 feet in length, and while larger barges may be built, the greater the length the greater are the problems therewith.
The art has, in addition, described fabricating an offshore structure at one location in sections, floating the sections on one or more vessels or barges, launching the sections into water at or near another location for positioning the offshore platform, aligning and connecting the sections together and then sinking the connected sections to form a support for a platform.